The components that are used to generate and transfer electrical energy to end users are well known in the art. Electrical power producers generally generate electrical power at very high initial voltages. Handling of such high voltages requires substantial electrical insulation. The insulation requires control of heat that is generated from the transmission of the electrical energy and maintenance of its dielectric properties.
The primary purpose of the types of fluids used in electrical transformers and fluid-filled transmission lines, hereinafter referred to as electrical insulating fluid or dielectric coolants, is to maintain cooling properties and fluid characteristics while in use within the system so as to maintain appropriate temperature as well as dielectric strength on demand. The heat of the transformer unit, for example, can increase to high levels for extended periods of time, which the fluid must be able to tolerate the heat without deterioration of properties. Additionally, the operation of transformers and the process of heat dissipation at various ambient temperatures subject the fluid to constant stresses.
It has been found that certain fluids have high electrical insulating and heat dissipation properties. These fluids are used with such electrical components as transformers and fluid filled transmission lines. One particular problem, even with such fluids, is that over time and with substantial exposure to high voltage electricity, their beneficial characteristics, such as insulating and/or heat dissipation properties, can degrade.
The industry uses a variety of insulating fluids which are easily available and cost effective. Examples are mineral oil, silicone fluid and synthetic hydrocarbon oils used in transformers, power cables and capacitors. Such fluids have certain properties that allow them to function satisfactorily, including that they are electrically insulating and dissipate heat, and resist break-down. However, some commonly used fluids pose safety or contamination concerns, and can be toxic to humans and animals. Many electrical components holding such fluids are situated near water or waterways where leakage or spills can cause serious damage to water and marine life. Leaks or spills on land can threaten ground water and contaminate soil.
Most conventional fluids are petroleum based and thus are derived from non-renewable starting materials. The amount of fluid of this type in use is significant. For example, one 15 MVA transformer (serving approximately 2000 customers, both residential and commercial) requires on the order of 3,600 gallons of electrically insulating fluid. One mile of fluid filled transmission cable (6 inch diameter) requires about 7,000 gallons. There are approximately 20,000 miles of high-pressure fluid filled transmission cables in the United States, most in larger cities and therefore near water or waterways.
Significant amounts of resources, both time and money, are spent by electrical power companies, in designing and implementing plans and systems to deter leaks or spills and to monitor transformers and transmission cables of these types for leaks or spills. It is estimated such costs are in the millions of dollars in the United States alone. Additionally, substantial resources are expended in reporting leaks or spills, even minor ones, because of environmental rules and regulations, at least with regard to petroleum based fluids. The effect of leaks or spills can be very costly, as can remediation of the same.
Therefore, there have been attempts to look to new sources for such fluids. It is desirable, with regard to such new sources, to address the environmental concerns as well as the issue of renewability of source.
Among the properties that are desirable for useful and efficient electrical insulation fluids are high dielectric breakdown voltage, low dissipation factor, high specific heat, high thermal conductivity, low coefficient of expansion, low viscosity, low sensitivity of viscosity to temperature, low pour point temperatures, low volatility, high flash point and low moisture. The electrical insulation fluids of the present invention possess a wide variety of these desirable properties.
Another demand placed upon electrical insulation fluids is that they maintain a certain degree of stability in terms of insulating properties despite some of the physical and chemical changes that take place during extended use.
Co-owned US Patent Application Publication 2006/0192185 describes electrical apparatuses and a method for their production, the apparatuses containing electrical insulation fluids comprising polytrimethylene homo- or copolyether glycol having a dielectric breakdown voltage greater than about 30 kV, wherein from about 50 to 100 mole percent of the repeating units of the polytrimethylene homo- or copolyether glycol are trimethylene ether units.